Factors that are attributable to be the cause for chromosomal diseases and the cells' ability to encounter their damages are under investigation. Fibroblast cells derived from patients afflicted with the genetic diseases, xeroderma pigmentosum and ataxia telangiectasia, which showed repair deficiency toward UV and X-radiation DNA lesions, respectively, will continue to be used, along with mutant CHO cells isolated in this laboratory specifically for alterations in DNA repair capacity. Emphasis for study in the coming year will be placed on (1) the completion of structural analysis for genes coding for basic chromosomal proteins, the histones, (2) continue with sequence determination of genes for metallothionein, which may be involved in cellular detoxification and (3) perfect an assay procedure with which DNA repair enzymes can be localized and quantitated in cultured cells.